The present invention generally relates to an intravenous cardiac lead and method having an improved configuration for fixing the lead in a desired position within a vein or an artery after implantation. The present invention is more particularly directed to such an intravenous lead for use with an implantable atrial defibrillator which provides cardioverting electrical energy to the atria of the heart when the heart is in need of cardioversion. The intravenous cardiac lead of the present invention is particularly adapted for implantation in the coronary sinus of the heart and includes at least one electrode adapted to be within the coronary sinus or great vein of the heart and a second electrode adapted to be within the right atrium of the heart when the lead is fed into the heart to a preferred position to enable the sensing of atrial activity of the heart and the delivery of the cardioverting electrical energy to the atria.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistent to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator with an external magnet.
Improved implantable atrial defibrillators and lead systems which exhibit automatic operation are fully described in copending U.S. applications, Ser. No. 07/685,130, filed Apr. 12, 1991, in the names of John M. Adams and Clifton A. Alferness for IMPROVED ATRIAL DEFIBRILLATOR AND METHOD, now U.S. Pat. No. 5,282,837, and Ser. No. 07/856,514, filed Mar. 24, 1992, in the names of John M. Adams, Clifton A. Alferness, and Paul E. Kreyenhagen for IMPROVED ATRIAL DEFIBRILLATOR, LEAD SYSTEMS, AND METHOD, which applications are assigned to the assignee of the present invention and incorporated herein by reference. The atrial defibrillators disclosed in the aforementioned referenced applications are truly automatic by including an atrial fibrillation detector which, responsive to sensed atrial activity, determines when the atria of the heart are in need of cardioversion. When the atrial fibrillation detector determines that the atria are in fibrillation and thus in need of cardioversion, the atrial fibrillation detector causes a cardioverter stage to deliver defibrillating or cardioverting electrical energy to the atria in timed relation to a detected ventricular electrical activation (R wave) of the heart. As a result, the atria are automatically and safely cardioverted.
As also disclosed in the aforementioned cross-referenced application, the quantity of electrical energy which is required to cardiovert or defibrillate the atria is reduced by an intravenous lead having an electrode adapted to be within the right atrium and another electrode adapted to be within the coronary sinus beneath the left atrium. The application of the cardioverting electrical energy across these electrodes not only reduces the energy required to cardiovert the atria, but also reduces the amount of energy applied to the ventricles. To place the electrodes in the positions noted above, the lead is fed down the superior vena cava, into the right atrium, through the coronary sinus ostium, and advanced into the coronary sinus.
While the lead is preshaped to conform to the above noted path after implantation to fix the lead in place, it would be desirable to provide the lead with more positive fixation since the blood flow through the coronary sinus is in a direction which tends to force the lead in a reverse direction with respect to the implantation feed path. Such positive fixation, however, must permit adequate blood flow through the coronary sinus and not cause occlusions.
The present invention provides such positive fixation for an intravenous lead such as the lead described above. In accordance with the present invention, the lead fixation is provided by a preformed section of the lead which has a resiliently coiled configuration. After the lead is implanted within a vein or an artery, the preformed section is permitted to assume its coiled configuration for making substantially continuous surface contact with inner wall surfaces of the artery or vein in the region of the coiled section. Such surface contact fixes the lead in place. Thereafter, fibrous tissue which builds up around the lead assures permanent fixation.